The principal objective of this study is to identify environmental and/or genetic risk factors for amyotrophic lateral sclerosis (ALS). We are addressing this objective by conducting a case-control study of ALS in the Northern California Kaiser Permanente Medical Care Program (KPMCP). Over a four-year period, approximately 175 persons newly diagnosed with ALS will be identified and recruited through physician referrals and computerized mechanisms available within the Kaiser system. The patients with ALS will be compared to a sample of 350 age- and gender-matched persons without ALS from the same membership. Specific study aims are as follows: (1) to investigate the association of ALS with exposure to neurotoxicants including lead, other heavy metals, solvents and pesticides; (2) to determine whether inadequate oxidative defenses for protecting against free-radicals enhance the toxicity of exogenous exposures; (3) to examine the evidence for familial aggregation of neurodegenerative diseases among first-degree relatives of patients with ALS; and (4) to estimate the incidence of ALS in diverse racial and ethnic groups.